PARALLEL AIRWAYS INHOMOGENEITY AND LUNG-TISSUE MECHANICS IN TRANSITION TO CONSTRICTED STATE IN RABBITS

To investigate whether changes of tissue resistance (Rti) during metha choline (MCh)-induced constriction correspond to an intrinsic mechanis m or are an artifact of increased airways inhomogeneity, rabbits were studied after exposure to air (n = 7) or 1.5 parts/million O-3 (n = 6) . Animals were anesthetized and mechanically ventilated. Tracheal flow and pressure (Ptr) and four alveolar capsule pressures (Pcap) were me asured during 3 min after administration of an intrajugular bolus of 0 .8 mg/ml MCh. By adjustment of the equation of motion [P(t) = E.V(t) R.dV(t)/dt + Po] [where P(t), V(t), and dV(t)/dt are pressure, volume , and flow as a function of time, respectively, E is elastance, R is r esistance, and P-0 is end-expiratory pressure] to Ptr, lung resistance (RL) and dynamic elastance (EL) were determined breath by breath. Rti and airways resistance (Raw) were determined from Pcap in phase with rate of change of pulmonary expansion. Hysteresivity (eta) was calcula ted. Parallel inhomogeneity was estimated from the coefficients of var iation (CV) of every Pcap at end inspiration and end expiration. Incre ase in CV significantly lagged Rti, RL, and eta. A linear relationship between EL and Raw was observed. Our results suggest that changes in tissue mechanics during the transition to the constricted state are no t artifactual.